257. Longest Consecutive Sequence

Medium · Hash Table

Given an unsorted array of integers, return the length of the longest consecutive elements sequence. Your algorithm must run in O(n) time.

Examples

Example 1
Input: nums = [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: [1,2,3,4] is the longest consecutive sequence

Constraints

• 0 ≤ n ≤ 10⁵